There have heretofore been many proposals concerning the preparation of solid titanium catalyst components containing magnesium, titanium and halogen as essential ingredients. It has been known that olefin polymerization catalysts containing such a solid titanium catalyst component and an organometallic compound component of a metal belonging to Group I to III in the periodic table exhibit excellent activity in olefin polymerization. However, further improvement has been desired in the polymerization activity of such olefin polymerization catalysts and powder properties of olefin polymers, especially olefin copolymers obtained by using such catalysts.
For example, when there was tried the preparation of olefin polymer particles consisting of a crystalline olefin polymer portion and an amorphous olefin polymer portion using such an olefin polymerization catalyst as described above, the polymer particles sometimes showed an increase in adhesion among the particles and a decrease in their particle flowability with an increase in the amount of amorphous olefin polymer portion (rubber portion) in the polymer particles. The polymer particles sometimes still more adhere together and markedly lowered their particle flowability when the polymer particles were subjected to steam treatment to deactivate the catalyst component therein, when the polymer particles were heated to remove volatile component therein, or when dried by heating.
Accordingly, it has been desired to make appearance of the olefin polymerization catalysts which is capable of producing olefin polymer particles tending not to show deterioration of their particle flowability caused by adhesion among the particles even when they contain a large amount of an amorphous olefin polymer portion.
The present inventors have carried out intensive research on the preparation of olefin polymer particles showing low adhesion among them and having good particle distribution and excellent particle properties even when they contain a large amount of an amorphous olefin polymer portion. As a result of prosecuting the research, it has been found that polymer particles as described above can be obtained by employing solid catalyst components for olefin polymerization formed by prepolymerization of olefin on an olefin polymerization catalyst comprising a solid catalyst component, an organometallic compound and, if necessary, an electron donor, in suspension in a liquid .alpha.-olefin or .alpha.-olefins, wherein at least two types of .alpha.-olefin including said liquid .alpha.-olefin is prepolymerized, in a specific amount, and a first olefin is prepolymerization catalyst component according to the present invention and a process for olefin polymerization using said catalyst have thus been completed.
Furthermore, it has been found that the above-described object can be achieved by employing a solid catalyst component for olefin polymerization formed by prepolymerizing a specific amount of at least two types of .alpha.-olefin on an olefin polymerization catalyst comprising a solid catalyst component, an organometallic compound and, if necessary, an electron donor, in suspension in a hydrocarbon solvent, and a second olefin polymerization catalyst component according to the invention and a process for olefin polymerization using said catalyst component have thus been completed.